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/*
* privileges.go - Functions for managing users and privileges.
*
* Copyright 2017 Google Inc.
* Author: Joe Richey (joerichey@google.com)
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
// Package security manages:
// - Cache clearing (cache.go)
// - Keyring Operations (keyring.go)
// - Privilege manipulation (privileges.go)
// - Maintaining the link between the root and user keyrings.
package security
import (
"log"
"os/user"
"github.com/pkg/errors"
"golang.org/x/sys/unix"
"github.com/google/fscrypt/util"
)
// SetThreadPrivileges drops drops the privileges of the current thread to have
// the uid/gid of the target user. If permanent is true, this operation cannot
// be reversed in the thread (the real and effective IDs are set). If
// permanent is false, only the effective IDs are set, allowing the privileges
// to be changed again with another call to SetThreadPrivileges.
func SetThreadPrivileges(target *user.User, permanent bool) error {
euid := util.AtoiOrPanic(target.Uid)
egid := util.AtoiOrPanic(target.Gid)
var ruid, rgid int
if permanent {
log.Printf("Permanently dropping to user %q", target.Username)
ruid, rgid = euid, egid
} else {
log.Printf("Temporarily dropping to user %q", target.Username)
// Real IDs of -1 mean they will not be changed.
ruid, rgid = -1, -1
}
// If setting privs to root, we want to set the uid first, so we will
// then have the necessary permissions to perform the other actions.
if euid == 0 {
if err := setUids(ruid, euid); err != nil {
return err
}
}
if err := setGids(rgid, egid); err != nil {
return err
}
if err := setGroups(target); err != nil {
return err
}
// If not setting privs to root, we want to avoid dropping the uid
// util the very end.
if euid != 0 {
if err := setUids(ruid, euid); err != nil {
return err
}
}
return nil
}
func setUids(ruid, euid int) error {
err := unix.Setreuid(ruid, euid)
log.Printf("Setreuid(%d, %d) = %v", ruid, euid, err)
return errors.Wrapf(err, "setting uids")
}
func setGids(rgid, egid int) error {
err := unix.Setregid(rgid, egid)
log.Printf("Setregid(%d, %d) = %v", rgid, egid, err)
return errors.Wrapf(err, "setting gids")
}
func setGroups(target *user.User) error {
groupStrings, err := target.GroupIds()
if err != nil {
return util.SystemError(err.Error())
}
gids := make([]int, len(groupStrings))
for i, groupString := range groupStrings {
gids[i] = util.AtoiOrPanic(groupString)
}
err = unix.Setgroups(gids)
log.Printf("Setgroups(%v) = %v", gids, err)
return errors.Wrapf(err, "setting groups")
}
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